1. Field of the Invention
The present invention relates to superconducting electron devices and more particularly to a quantum interference transistor utilizing superconducting channel.
2. Description of the Prior Art
So far Josephson junction devices have been proposed as electron devices using a superconductor. The Josephson junction device is essentially of a two-terminal element so that it is difficult to use the same in practice. Also, it may be considered to make the Josephson junction device as a quasi-3-terminal device. However, the structure for this becomes complicated so that it is difficult to apply such a modified device to an integrated circuit.
Further, as a 3-terminal superconducting electron device, there is proposed a transistor by forming source and drain electrodes formed of a superconducting material on a semiconductor body. The leaked Cooper pairs from the electrodes are controlled by an application of a gate voltage relative to the source electrode to control the current of Cooper pair. However, the device is essentially regarded as a semiconductor device.
Furthermore, it is proposed that the device is operated just like a metal gate type field-effect-transistor (FET) using superconductor, i.e., so-called MES-FET (Metal Semiconductor-FET). This previously-proposed element merely utilizes the superconductor as a resistor having a low electric resistivity, and it does not effectively utilize its coherency which is one of the major characteristics in the superconductor.
It should be noted that the prior art electron device using the superconductivity is operated on the basis of a transition between a superconducting state and a non-superconducting state which are made corresponding to a binary state of "0" and "1". In other words, since the prior art superconducting electron device is not operated only in the superconducting state, in the prior art device, a transition speed at which it returns at least from the non-superconducting state to the superconducting state is substantially the same as that of the regular device which does not utilize the superconductor. Thus, this kind of superconducting electron device is restricted in increasing its operation speed.
On the other hand, a quantum interference transistor (QUIT) utilizing Aharanov-Bohm effect was reported at the IEDM (International Electron Device Meeting) '86, pp. 76 to 79. According to the QUIT which does not use a superconducting substance, however, a single electron is a charge carrier and discharges a phonon at a high temperature. Hence, energy relaxation occurs and loses coherency. Thus, such a QUIT cannot be operated in the presence of a phonon scattering.